Hi Jon, Nice summary of the various encoders and their applications to motors. I'll be sharing this material with my Controls Systems class at ITT Tech along with the encoder handbook. I look forward to reading your column on resolvers.

Jon, excellent article. I do considerable work in designing and developing work cells for robotic systems. Rotary and linear encoders are extremely valuable and accurate and provide just about the only reliable method for determining shaft position--which is critical to the function of the equipment. Having a basic understanding of how they work is paramount when trying to bring about a "fix" or troubleshooting a problem. Many thanks for the information.

I don't know about you, but it seems to me that industry in general is really starting to confuse those two words. I've seen ads for "analog encoders" that talk about their internal technologies that perfectly describe a resolver. (I also dont' think the 90% of recent college graduates could define one difference).

I have only heard of rotary magnetic coupled devices called resolvers. The two versions that I have seen are an exciter input and sine and cosine outputs, or sine and cosine inputs and a resultant output. Another component used with encoders in robotics is the revolution counter - the motor may turn many rotations in an axis' range of motion.

Switched-capacitor filters have a few disadvantages. They exhibit greater sensitivity to noise than their op-amp-based filter siblings, and they have low-amplitude clock-signal artifacts -- clock feedthrough -- on their outputs.

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